1. Field of the Invention
The present invention relates to a coil electric conductor and a laminated coil electric conductor which are used in various kinds of electronic components such as transformers and choke coils. The invention further relates to a production method for these conductors as well as an electronic component using these conductors.
2. Background Art
Related-art production methods for coil electric conductors are described in Japanese Patent Unexamined Publication No. 2001-267166 (hereinafter referred to as Patent Document 1) and H11-204361 (hereinafter referred to as Patent Document 2).
FIG. 16A to FIG. 16E are cross-sectional views showing a production method for a coil electric conductor, which is described in Patent Document 1.
First, in a background conductive layer forming process (FIG. 16A), background conductive layer (hereinafter referred to as the background layer) 51 is formed on insulating substrate 50. In a resist pattern forming process (FIG. 16B), resist pattern 52 is formed so that a face of background layer 51 is spirally exposed. In a first electroplating process (FIG. 16C), electroplating using background layer 51 as a background is performed and central conductor (hereinafter referred to as conductor) 53 having a substantially rectangular cross section is formed. In a resist pattern peeling process (FIG. 16D), resist pattern 52 is peeled. In a second electroplating process (FIG. 16E), electroplating using conductor 53 as a background is performed and conductive face layer (hereinafter referred to as conductive layer) 54 is formed. In this manner, coil electric conductor 55 made of conductor 53 and conductor layer 54 which coats conductor 53 is produced.
However, coil electric conductor 55 is formed so that conductor layer 54 coats conductor 53, by means of the electroplating using conductor 53 as a background, and since the circulation in a plating bath for electroplating varies according to individual patterns of coil electric conductor 55, variations occur in the concentration distribution in the plating bath. Furthermore, plating layers become thin at positions remote from a power supply section (not shown). For this reason, the cross-sectional shape of coil electric conductor 55 is difficult to produce with high precision.
The cross-sectional shape of coil electric conductor 55 should be originally uniform in any section thereof. However, variations in precision cause nonuniformity of the cross-sectional shape. As a result, the conductivity of coil electric conductor 55 lowers. Precision is improved by reducing the current during electroplating, but this increases the operating time and lowers productivity.
Furthermore, since background layer 51 is peeled by etching after the resist pattern peeling process (FIG. 16D), the production process becomes complicated. In addition, if background layer 51 is not completely peeled, adjacent turns of coil electric conductor 55 are easily connected and electrically short-circuited.
Furthermore, the turns of coil electric conductor 55 are juxtaposed at narrow intervals, so that some of the turns of coil electric conductor 55 are easily brought into contact with one another and electrically short-circuited, by external impact during mounting of coil electric conductor 55.
In addition, if an electronic component using coil electric conductor 55 is used for a long time, a metal constituent used in coil electric conductor 55 moves through the faces of an insulator. As a result, mutually adjacent turns of coil electric conductor 55 or coil electric conductor 55 and other electronic components can cause short-circuits or insulating failures; that is to say, a migration phenomenon occurs. In addition, it is generally recommended that the same kind of material be used as the constituent material of each of conductor 53 and conductor layer 54, and a material of high conductivity is used for conductor 53 and conductor layer 54 in order to improve the conductivity of coil electric conductor 55. However, in general, metals of high conductivity tend to easily cause a migration phenomenon. Accordingly, if a material which does not easily cause a migration phenomenon is used for conductor 53 and conductor layer 54, the conductivity of coil electric conductor 55 becomes low.
FIGS. 17A to 17G are cross-sectional views showing a production method for a coil electric conductor, which is described in Patent Document 2.
First, background thin film layer (hereinafter referred to as background layer) 57 is formed on insulating substrate 56 (FIG. 17A). Then, positive photo resist layer (hereinafter referred to as resist layer) 58 is laminated on background layer 57 (FIG. 17B). Then, positive photo resist mask pattern (hereinafter referred to as the mask) 59 is formed from resist layer by a photolithography method (FIG. 17C). Then, coil electric conductor plating layer (hereinafter referred to as plating layer) 61 having a mushroom-shaped cross section is formed by electroplating. Plating layer 61 grows and is formed on both exposed section 60 of background layer 57 and mask 59 close to exposed section 60 (FIG. 17D). Then, protecting metal thin film layer (hereinafter referred to as protective layer) 62 which coats the whole of plating layer 61 is formed by electroplating (FIG. 17E). Then, the whole face of protective layer 62 is irradiated with activating radiation, whereby mask 59 exposed through gap 63 in plating layer 61 is developed and removed (FIG. 17F). Furthermore, background layer 57 is removed by etching (FIG. 17G). In this manner, coil electric conductor 64 made of background layer 57, plating layer 61 and protective layer 62 is produced.
Background layer 57 on insulating substrate 56 is electroplated, whereby plating layer 61 grows and coil electric conductor 64 is formed. Furthermore, protective layer 62 formed by electroplating coats a face of plating layer 61. As described above, in the case of electroplating, coil electric conductor 64 having a mushroom-shaped cross section is difficult to produce with high precision. In addition, the cross-sectional shape of coil electric conductor 64 becomes non-uniform.
In addition, after the coating of protective layer 62, mask 59 is peeled by exposure and development, and background layer 57 is peeled by etching, so that the production process becomes complicated. Furthermore, if background layer 57 is not completely peeled, electrical short-circuiting easily occurs.
Furthermore, the adjacent turns of coil electric conductor 64 are juxtaposed at narrow intervals, so that some of the adjacent turns of coil electric conductor 64 are easily brought into contact with one another and electrically short-circuited, by external impact during mounting of coil electric conductor 64.